Ceramic bodies made from metal oxide powders have been used for some time in making dental articles, because of good biocompatibility and stability under load. These ceramic bodies have been typically processed by machining, for example, a green compact or a sintered body using a milling cutter. Green compacts have been made by compacting the metal oxide powder using cold isostatic or uniaxial pressing methods. After machining, the green compact must be sintered to achieve final properties. Sintered bodies have been made by hot isostatic processing whereby the starting metal oxide powder is simultaneously compacted and sintered.
Aluminum oxide has been particularly important, although zirconia has been considered, because it has greater mechanical strength than aluminum oxide. Tetragonal zirconia has exceptional mechanical strength due to a phase transformation mechanism that is triggered when a crack propagates into the material, causing the crack to be arrested. However, tetragonal zirconia is presently found to be opaque, thus limiting this material from applications requiring higher translucency, such as dental applications. Translucent cubic zirconia is known, but it has relatively low mechanical strength. Therefore, there is a continuing need for ceramic bodies that have both high strength and translucency.